Planktic Foraminiferal Test Size and Weight Response to the Late Pliocene Environment

Abstract

Atmospheric carbon dioxide (pCO 2 atm ) is impacting the ocean and marine organisms directly via changes in carbonate chemistry and indirectly via a range of changes in physical parameters most dominantly temperature. To assess potential impacts of climate change on carbonate production in the open ocean, we measured size and weight of planktic foraminifers during the late Pliocene at pCO 2 atm concentrations comparable to today and global temperatures 2 to 3°C warmer. Size of all foraminifers was measured at Atlantic Ocean Deep Sea Drilling Project (DSDP) Site 610, Ocean Drilling Program (ODP) Site 999, and Integrated Ocean Drilling Program (IODP) Site U1313. Test size was smaller during the Pliocene than in modern assemblages under the same environmental conditions. During the cold marine isotope stage (MIS) M2, size increased at Site 999, potentially linked to intensified stratification of the surface ocean in response to the closure of the Central American Seaway. At Site U1313, test size tracks the warming throughout the late Pliocene. Size-normalized weight (SNW) of Globigerina bulloides at Site U1313 decreased during warmer temperature intervals. SNW of Globigerinoides ruber (white) at Site 999 displays high-frequency variability not correlated to temperature. Yet during the glacial period within MIS M2, test weight was higher during higher temperatures. Our results support studies in the modern ocean, which challenge the view that carbonate chemistry is the primary driver for calcification. To better understand processes driving changes in SNW, computer tomography was used to quantify calcite to volume ratios. During interglacial periods, lower calcite volume but higher test volume suggests less suitable conditions for calcification. As this signal is not evident in SNW, subtle changes in calcification might not be observed by the weight-based method.Plain Language Summary Calcium carbonate shell-producing organisms in the oceans are in danger of losing the ability to build shells because oceans are becoming warmer and more acidic from absorbing the excess carbon dioxide in the atmosphere. Here we measure the size and weight of microscopic plankton shells during a past climate interval about three million years ago when the atmospheric carbon dioxide level was similar to today. Studying this time interval allows us to quantify impacts of a warmer more acidic ocean on the ability of plankton in the ocean to produce carbonate. During this interval, temperature fluctuated, and local environmental conditions changed in response to the emergence of the Isthmus of Panama. We show here that both size and weight react to global and local drivers, which include but are not limited to temperature.

Atmospheric CO2 during the Mid-Piacenzian Warm Period and the M2 glaciation

“…However, while our chosen species for pH/CO 2 reconstruction, G. ruber, is known to be relatively susceptible to partial dissolution on the seafloor 43 , its δ 11 B signal has been observed to be robust 14,44 . Furthermore, a recent study 45 of test weight and fragmentation at ODP 999 showed that tests become better preserved during M2 ( Supplementary Fig. 7), as observed during glacial periods of the late Pleistocene 46 .…”

Shell density of planktonic foraminifera and pteropod species Limacina helicina in the Barents Sea: Relation to ontogeny and water chemistry

“…Both PF and L. helicina are sensitive to the carbonate chemistry in their environment and the extent of their calcification is commonly used as an indicator for OA [33][34][35][36][37][38][39][40]. Furthermore, due to their long sedimentary record PF shell density has been used for paleoceanographic studies of OA and atmospheric CO 2 [41][42][43][44].…”

Enhanced Carbonate Dissolution Associated With Deglacial Dysoxic Events in the Subpolar North Pacific

“…In addition, other aspects of the growth habitat, including temperature, salinity, and food availability, may drive changes in foraminiferal growth and calcification, and thus influence SNW (Beer et al, 2010b;Bijma et al, 1990;Broecker & Clark, 2001;de Villiers, 2004;Pak et al, 2018;Todd et al, 2020;Weinkauf et al, 2016). In some paleoceanographic records, dissolution proxies such as fragmentation counts and external smoothing of shell features show a decoupling between dissolution and SNW (Davis et al, 2016;Pak et al, 2018;Todd et al, 2020 counts as an independent measure of dissolution and found that variation in SNW could not be explained by variation in dissolution intensity and instead interpreted SNW in terms of local growth conditions. In the Santa Barbara Basin (SBB) prior to 1975, G. bulloides SNWs were highest during times with upwelling of cool waters with lower Ω and showed no external signs of dissolution, suggesting that growth responses to temperature had a greater influence on SNW than carbonate chemistry (Pak et al, 2018).…”

“…For example, lower carbonate ion and pH conditions leads to lower calcification, and thus lower SNW, in at least some species (Bijma et al, 2002;Marshall et al, 2013;Moy et al, 2009). In addition, other aspects of the growth habitat, including temperature, salinity, and food availability, may drive changes in foraminiferal growth and calcification, and thus influence SNW (Beer et al, 2010b;Bijma et al, 1990;Broecker & Clark, 2001;de Villiers, 2004;Pak et al, 2018;Todd et al, 2020;Weinkauf et al, 2016). In some paleoceanographic records, dissolution proxies such as fragmentation counts and external smoothing of shell features show a decoupling between dissolution and SNW (Davis et al, 2016;Pak et al, 2018;Todd et al, 2020 counts as an independent measure of dissolution and found that variation in SNW could not be explained by variation in dissolution intensity and instead interpreted SNW in terms of local growth conditions.…”